The present invention relates to an injection syringe of the type comprising a syringe body bearing an injection needle, a reservoir containing a liquid to be injected, which reservoir comprises a moving part mounted so that it can move in sliding with respect to the body so as to cause the liquid to be injected to flow down the injection needle, and a moving needle protector mounted so that it can be moved with respect to the injection needle under the control of a spring, from a retracted position set back from the injection end of the needle to an active protective position in which the front end of the protector is forward of the injection end of the needle, the syringe further comprising means for, during injection, retaining a first end of the spring collaborating with the protector, and means carried by the said moving part for, at the end of injection, releasing the said first end of the spring to cause the protector to move into its active protective position.
Document EP-A-0 467 173, for example, discloses a syringe of the aforementioned type. In a syringe such as this, the needle protector is arranged around the syringe body, of which it constitutes a sheath. The spring that operates the needle protector is initially compressed between the syringe body and the sheath. The sheath is held onto the syringe body by elastic snap-fastening. The syringe piston comprises means for detaching the sheath from the syringe body, which releases the spring and moves the sheath into its active protective position.
As the spring is initially compressed, it has to be compressed during the manufacture of the syringe, which makes it tricky to fit. In addition, as the spring is kept compressed during syringe storage, this spring may experience premature ageing, reducing its performance over time.
The object of the invention is to provide an injection syringe equipped with a spring-loaded needle protector which does not exhibit the abovementioned drawbacks and which, in particular, is easy to produce and is reliable.
To this end, the subject of the invention is an injection syringe of the aforementioned type, characterized in that the second end of the spring is pressed against the said part of the reservoir that can move with respect to the body to gradually compress the spring during injection.
According to some particular embodiments, the injection syringe has one or more of the following features:
the said moving part comprises a cylindrical wall closed off by an end forming a reservoir in which there is mounted, so that it can slide, a piston through which the said injection needle passes, the body comprising means for immobilizing the piston at least during injection;
the injection needle extends over most of the length of the body;
the said spring is inserted between the said moving part and the protector and the said means for retaining the first end of the spring comprise means for immobilizing the protector with respect to the body, the said means for releasing the first end of the spring comprising means for releasing the protector against which the said first end of the spring rests;
the protector comprises an end ring extended by legs extending partially up inside the body, the said means for immobilizing the protector comprise complementing projecting and recessed locking profiles borne by the body and the legs, and the said means for releasing the protector comprise means for deforming the legs with a view to disengaging the projecting and recessed complementing profiles; and
the deforming means comprise, borne by the legs, cam surfaces designed to collaborate with the end of the said moving part.